First-principles Calculations Of Novel Non-magnetic Topological Materials

Topological materials have received growing attention over recent years for their elec-tronic structures with non-trivial topology in momentum space.Based on the distinct type of electronic structures,topological materials have been classified into topological insulators and topological semimetals that exhibit robust boundary states and quantized bulk responses,which can be used for an array of applications,from information storage to quantum compu-tation and spintronic devices.Based on symmetry indicators,the topological properties of materials in the inorganic crystal structure database have been investigated.While topolog-ical materials with promising applications are rare,and thus it is necessary to investigated new materials by First-principles calculations,which have been demonstrated unprecedented predictive power for topological material selection and design.In the thesis,we investigate the topological characters of new materials based on the first-principles calculations.First,I introduce the background of topological matter states,including the quantum Hall effect,topological insulators,topological semimetals with linear dispersion and topological Lut-tinger semimetals.Secondly,I introduce some theories and methods used in this thesis,in-cluding first-principles calculations based on density functional theory,Wannier functions,and k·p model.Finally,I will give my research on non-magnetic topological materials as follows:In Chapter 3,a new class of topological insulators with large band gap and single Dirac cone are designed and investigated.By means of a ternary chemical potential phase diagram and phonon spectrum calculations,we propose that MTl₄Te₃（M=Cd,Hg）are thermo-dynamically and dynamically stable in the body-centered tetragonal crystal structure with I4/mcm symmetry.Our electronic structure calculations confirm that a robust s-p band in-version occurs in MTl₄Te₃atΓpoint,and a topological band gap of 0.13 e V in Cd Tl₄Te₃is induced by the spin-orbit coupling.As a result,one single Dirac cone formed by the topolog-ical surface states is discovered in the bulk gap on the（100）surface.These results suggest that MTl₄Te₃are ideal three-dimensional topological insulators that are synthesizable in experiment and could be used to design efficient spin torque equipment and spin devices.In Chapter 4,the electronic and topological properties of BC8-Si are systematically studied.Based on the first-principles calculations and k·p model analysis,our results demonstrate that BC8-Si is a topological Luttinger semimetal with parabolic parabolic dis-persive topological surface states.Moreover,a complete phase diagram of the body-centered silicon（BC8-Si）via lattice constant a and internal atomic coordinate x is explored,which demonstrates that the electronic and topological properties of BC8-Si are sensitive to the a and x.The topological Luttinger semimetal can be further tuned to a normal insulator or topological Dirac semimetal by very tiny changing of a and x.These results successfully explain the contradictory transport reports of BC8-Si in experiments.More importantly,the topological surface states are reported for the first time in the synthesized allotrope of sili-con,which provides an opportunity to integrate the topological quantum devices and silicon chips together.Chaper 5 gives the conclusion and expectation of this thesis.